Longitudinal proneuroactive and neuroactive steroid profiles in medication-free women with, without and at-risk for perinatal depression: A liquid chromatography-tandem mass spectrometry analysis

BACKGROUND

Neuroactive steroids (NAS) are derivatives of cholesterol or steroidal precursors made in the gonads, adrenal gland, placenta and brain. We characterized longitudinal plasma proneuroactive and NAS in healthy perinatal comparison women (HPCW), women at-risk for perinatal depression (AR-PND), and women with PND with/without comorbid anxiety. We hypothesized that AR-PND women who either did or did not go on to develop PND would have elevated NAS concentrations as compared to HPCW and that NAS would be correlated to depressive and anxiety symptoms.

METHODS

A prospective cohort study evaluated 75 medication-free perinatal women (HPCW, n = 30; AR-PND, n = 19; PND, n = 26). Standardized depression and anxiety assessments and blood samples were completed across 5 visits. Structured Clinical Interviews for DSM-IV TR Disorders were administered at study entry and exit. Plasma pregnenolone, progesterone, 5α- and 5β-dihydroprogesterone, pregnanolone, allopregnanolone, deoxycorticosterone and tetrahydrodeoxycorticosterone were quantified by liquid chromatography-tandem mass spectrometry. Longitudinal relationships between risk-group, depression and anxiety symptoms, and NAS concentrations were analyzed using generalized estimating equations to control for repeated measures correlations.

RESULTS

Perinatal 5α-dihydroprogesterone, 5β-dihydroprogesterone, allopregnanolone, deoxycorticosterone, and tetrahydrodeoxycorticosterone concentrations were higher in AR-PND and PND women compared to HPCW (β = 3.57 ± 1.40 and β = 2.11 ± 1.12, p = 0.03; β = 0.18 ± 0.06 and β = 0.03 ± 0.05, p = 0.02; β = 1.06 ± 0.42 and β = 1.19 ± 0.47, p = 0.01; β = 0.17 ± 0.07 and β = 0.11 ± 0.06, p = 0.05; β = 0.03 ± 0.01 and β = 0.03 ± 0.01, p = 0.05, respectively). Perinatal allopregnanolone, 5α-dihydroprogesterone and tetrahydrodeoxycorticosterone were positively associated with HAM-D17 (all p < 0.02). HAM-A was positively associated with 5α- and 5β-dihydroprogesterone, pregnanolone, allopregnanolone, deoxycorticosterone and tetrahydrodeoxycorticosterone (all p < 0.05). A history of depression was associated with increased 5α-dihydroprogesterone (2.20 ± 1.09, p = 0.05), deoxycorticosterone (0.13 ± 0.06, p = 0.03) and tetrahydrodeoxycorticosterone (0.03 ± 0.01, p = 0.02).

CONCLUSION

To our knowledge, this study represents the largest prospective study of 5-α and 5-β reductase products of progesterone and deoxycorticosterone in HPCW and women AR-PND. Data suggest that PND is associated with both a reduction of progesterone to 5β-dihydroprogesterone, 5α-dihydroprogesterone, and allopregnanolone, and the 21-hydroxylation to deoxycorticosterone and tetrahydrodeoxycorticosterone. The shift towards 5α-dihydroprogesterone, deoxycorticosterone and tetrahydrodeoxycorticosterone was associated with a history of depression, a significant risk factor for PND.

Desoxycorticosterone pivalate-salt treatment leads to non-dipping hypertension in Per1 knockout mice

AIM

Increasing evidence demonstrates that circadian clock proteins are important regulators of physiological functions including blood pressure. An established risk factor for developing cardiovascular disease is the absence of a blood pressure dip during the inactive period. The goal of the present study was to determine the effects of a high salt diet plus mineralocorticoid on PER1-mediated blood pressure regulation in a salt-resistant, normotensive mouse model, C57BL/6J.

METHODS

Blood pressure was measured using radiotelemetry. After control diet, wild-type (WT) and Per1 (KO) knockout mice were given a high salt diet (4% NaCl) and the long-acting mineralocorticoid deoxycorticosterone pivalate. Blood pressure and activity rhythms were analysed to evaluate changes over time.

RESULTS

Blood pressure in WT mice was not affected by a high salt diet plus mineralocorticoid. In contrast, Per1 KO mice exhibited significantly increased mean arterial pressure (MAP) in response to a high salt diet plus mineralocorticoid. The inactive/active phase ratio of MAP in WT mice was unchanged by high salt plus mineralocorticoid treatment. Importantly, this treatment caused Per1 KO mice to lose the expected decrease or 'dip' in blood pressure during the inactive compared to the active phase.

CONCLUSION

Loss of PER1 increased sensitivity to the high salt plus mineralocorticoid treatment. It also resulted in a non-dipper phenotype in this model of salt-sensitive hypertension and provides a unique model of non-dipping. Together, these data support an important role for the circadian clock protein PER1 in the modulation of blood pressure in a high salt/mineralocorticoid model of hypertension.

GABAA receptor modulating steroid antagonists (GAMSA) are functional in vivo

GABAA receptor modulating steroid antagonists (GAMSA) selectively inhibit neurosteroid-mediated enhancement of GABA-evoked currents at the GABAA receptor. 3α-hydroxy-neurosteroids, notably allopregnanolone and tetrahydrodeoxycorticosterone (THDOC), potentiate GABAA receptor-mediated currents. On the contrary, various 3β-hydroxy-steroids antagonize this positive neurosteroid-mediated modulation. Importantly, GAMSAs are specific antagonists of the positive neurosteroid-modulation of the receptor and do not inhibit GABA-evoked currents. Allopregnanolone and THDOC have both negative and positive actions. Allopregnanolone can impair encoding/consolidation and retrieval of memories. Chronic administration of a physiological allopregnanolone concentration reduces cognition in mice models of Alzheimer's disease. In humans an allopregnanolone challenge impairs episodic memory and in hepatic encephalopathy cognitive deficits are accompanied by increased brain ammonia and allopregnanolone. Hippocampal slices react in vitro to ammonia by allopregnanolone synthesis in CA1 neurons, which blocks long-term potentiation (LTP). Thus, allopregnanolone may impair learning and memory by interfering with hippocampal LTP. Contrary, pharmacological treatment with allopregnanolone can promote neurogenesis and positively influence learning and memory of trace eye-blink conditioning in mice. In rat the GAMSA UC1011 inhibits an allopregnanolone-induced learning impairment and the GAMSA GR3027 restores learning and motor coordination in rats with hepatic encephalopathy. In addition, the GAMSA isoallopregnanolone antagonizes allopregnanolone-induced anesthesia in rats, and in humans it antagonizes allopregnanolone-induced sedation and reductions in saccadic eye velocity. 17PA is also an effective GAMSA in vivo, as it antagonizes allopregnanolone-induced anesthesia and spinal analgesia in rats. In vitro the allopregnanolone/THDOC-increased GABA-mediated GABAA receptor activity is antagonized by isoallopregnanolone, UC1011, GR3027 and 17PA, while the effect of GABA itself is not affected.

Neurosteroids in hepatic encephalopathy: Novel insights and new therapeutic opportunities

Hepatic encephalopathy (HE) is a serious neuropsychiatric disorder resulting from liver failure. Symptoms of HE include mild cognitive impairment, stupor and coma. Morphological changes to neuroglia (both astrocytes and microglia) occur in HE consisting of cytotoxic brain edema (astrocyte swelling) in acute liver failure and Alzheimer type-2 astrocytosis in cirrhosis. Visual-evoked responses in animals with liver failure and HE manifest striking similarities to those in animals treated with agonists of the GABA-A receptor complex. Neurosteroids are synthesized in brain following activation of translocator protein (TSPO), a mitochondrial neuroglial cholesterol-transporter protein. TSPO sites are activated in both animal models of HE as well as in autopsied brain tissue from HE patients. Activation of TSPO sites results in increased cholesterol transport into the mitochondrion followed by stimulation of a metabolic pathway culminating in the synthesis of allopregnanolone (ALLO) and tetrahydrodeoxycorticosterone (THDOC), neurosteroids with potent positive allosteric modulatory action on the GABA-A receptor complex. Concentrations of ALLO and THDOC in brain tissue from mice with HE resulting from toxic liver injury are sufficient to induce sedation in animals of the same species and significant increases in concentrations of ALLO have been reported in autopsied brain tissue from cirrhotic patients with HE leading to the proposal that "increased GABAergic tone" in HE results from that increased brain concentrations of this neurosteroid. Agents with the potential to decrease neurosteroid synthesis and/or prevent their modulatory actions on the GABA-A receptor complex may provide novel approaches to the management and treatment of HE. Such agents include indomethacin, benzodiazepine receptor inverse agonists and a novel series of compounds known as GABA-A receptor-modulating steroid antagonists (GAMSA).

Neurosteroids; potential underpinning roles in maintaining homeostasis

The neuroactive steroids which are synthesized in the brain and nervous system are known as "Neurosteroids". These steroids have crucial functions such as contributing to the myelination and organization of the brain connectivity. Under the stressful circumstances, the concentrations of neurosteroid products such as allopregnanolone (ALLO) and allotetrahydrodeoxycorticosterone (THDOC) alter. It has been suggested that these stress-derived neurosteroids modulate the physiological response to stress. Moreover, it has been demonstrated that the hypothalamic-pituitary-adrenal (HPA) axis mediates the physiological adaptation following stress in order to maintain homeostasis. Although several regulatory pathways have been introduced, the exact role of neurosteroids in controlling HPA axis is not clear to date. In this review, we intend to discern specific pathways associated with regulation of HPA axis in which neuroactive steroids have the main role. In this respect, we propose pathways that may be initiated after neurosteroidogenesis in different brain subregions following acute stress which are potentially capable of activating or inhibiting the HPA axis.

Successful treatment of a cat with primary hypoadrenocorticism and severe hyponatremia with desoxycorticosterone pivalate (DOCP)

A 6-year-old, castrated male Siamese cat was diagnosed with primary hypoadrenocorticism, confirmed by an adrenocorticotopic hormone (ACTH) stimulation test documenting both hypocortisolism and hypoaldosteronism. The cat was successfully treated using a combination of prednisolone and desoxycorticosterone pivalate (DOCP). This case demonstrates that DOCP can be used successfully as mineralocorticoid supplementation in cats with hypoadrenocorticism and may have a longer therapeutic duration than that in dogs.

Neurosteroidal modulation of in vitro epileptiform activity is enhanced in pilocarpine-treated epileptic rats

We employed field potential recordings in brain slices obtained from pilocarpine-treated epileptic (4-5weeks following a pilocarpine-induced status epilepticus) and age-matched, non-epileptic control (NEC) rats to establish the effects of the neurosteroid allotetrahydrodeoxycorticosterone (THDOC) on the epileptiform activity - including high frequency oscillations (HFOs; ripples: 80-200Hz, fast ripples: 250-500Hz) - induced by 4-aminopyridine (4AP) in piriform (PC) and entorhinal (EC) cortices. Both structures are highly susceptible to generate seizures and may also be involved in epileptogenesis. We found that THDOC application to pilocarpine-treated slices: (i) decreased interictal discharge frequency in PC while increasing it in EC; (ii) abolished ictal discharges in both areas in approx. one third of the experiments and reduced them in frequency and duration in the remaining experiments; and (iii) increased the occurrence of ripples and fast ripples associated to interictal events, and modified their pattern of occurrence during ictal discharges in both PC and EC. These effects were either weaker or absent in NEC tissue. Our results demonstrate that THDOC plays a structure-dependent modulatory role in epileptiform synchronization in the pilocarpine-treated epileptic rat brain where its actions are more pronounced than in NEC tissue. This evidence supports the application of neurosteroids as potential antiepileptic tools.

[11beta-Hydroxylation of 6alpha-Fluoro-16alpha-Methyl-Deoxycorticosterone 21-Acetate by filamentous fungi]

Selected filamentous fungi--98 strains of 31 genera--were screened for the ability to catalyze 11beta-hydroxylation of 6alpha-fluoro-16alpha-methyl-deoxycorticosterone 21-acetate (FM-DCA). It was established that representatives of the genera Gongronella, Scopulariopsis, Epicoccum, and Curvularia have the ability to activate 11beta-hydroxylase steroids. The strains of Curvularia lunata VKM F-644 and Gongronella butleri VKM F-1033 expressed maximal activity and formed 6lpha-fluoro-16alpha-methyl-corticosterone as a major bioconversion product from FM-DCA. The structures of the major products and intermediates of the bioconversion were confirmed by TLC, H PLC, MS and 1H NMR analyses. Different pathways of 6alpha-fluoro-16alpha-methyl-corticosterone formation by C. lunata and G. butleri strains were proposed based on intermediate identification. The constitutive character and membrane-binding localization were evidence of a 11beta-hydroxylating system in G. butleri, while an inducible character and microsomal localization was confirmed for 11beta-hydroxylase of C. lunata. Under optimized conditions, the molar yield of 6alpha-fluoro-16alpha-methyl-corticosterone reached 65% at a FM-DCA substrate loading of 6 g/L.

Modulation of neurosteroid potentiation by protein kinases at synaptic- and extrasynaptic-type GABAA receptors

GABAA receptors are important for inhibition in the CNS where neurosteroids and protein kinases are potent endogenous modulators. Acting individually, these can either enhance or depress receptor function, dependent upon the type of neurosteroid or kinase and the receptor subunit combination. However, in vivo, these modulators probably act in concert to fine-tune GABAA receptor activity and thus inhibition, although how this is achieved remains unclear. Therefore, we investigated the relationship between these modulators at synaptic-type α1β3γ2L and extrasynaptic-type α4β3δ GABAA receptors using electrophysiology. For α1β3γ2L, potentiation of GABA responses by tetrahydro-deoxycorticosterone was reduced after inhibiting protein kinase C, and enhanced following its activation, suggesting this kinase regulates neurosteroid modulation. In comparison, neurosteroid potentiation was reduced at α1β3(S408A,S409A)γ2L receptors, and unaltered by PKC inhibitors or activators, indicating that phosphorylation of β3 subunits is important for regulating neurosteroid activity. To determine whether extrasynaptic-type GABAA receptors were similarly modulated, α4β3δ and α4β3(S408A,S409A)δ receptors were investigated. Neurosteroid potentiation was reduced at both receptors by the kinase inhibitor staurosporine. By contrast, neurosteroid-mediated potentiation at α4(S443A)β3(S408A,S409A)δ receptors was unaffected by protein kinase inhibition, strongly suggesting that phosphorylation of α4 and β3 subunits is required for regulating neurosteroid activity at extrasynaptic receptors. Western blot analyses revealed that neurosteroids increased phosphorylation of β3(S408,S409) implying that a reciprocal pathway exists for neurosteroids to modulate phosphorylation of GABAA receptors. Overall, these findings provide important insight into the regulation of GABAA receptors in vivo, and into the mechanisms by which GABAergic inhibitory transmission may be simultaneously tuned by two endogenous neuromodulators.

Modulation of the human ρ1 GABAA receptor by inhibitory steroids

RATIONALE

Modulators of the ρ1 GABAA receptor may be useful in the treatment of visual, sleep, and cognitive disorders. Neuroactive steroids and analogues have been shown to modulate ρ1 receptor function, but the molecular mechanisms are poorly understood.

OBJECTIVES

We employed electrophysiology and voltage-clamp fluorometry to compare the actions of several neuroactive steroids and analogues on the human ρ1 GABAA receptor.

RESULTS

Results confirmed that P294S and T298F mutations affect modulation by steroids. The P294S mutation abolished inhibition by (3α,5β)-3-hydroxypregnan-20-one (3α5βP) while the T298F mutation eliminated inhibition by 17β-estradiol. Voltage-clamp fluorometry demonstrated that steroids differing in the presence of a charged group on C3 or nature of substituent on C17 uniquely modified fluorescence changes elicited by GABA in the extracellular domain. The I307Q mutation reversed the inhibitory effect of 3α5βP but was without effect on modulation by (3α,5β)-3-hydroxypregnan-20-one sulfate or 17β-estradiol. The effect of 3α5βP on the fluorescence change generated at Y241C was dependent on whether the steroid acted as an inhibitor or a potentiator. Further, the effect was limited to uncharged 5β-reduced steroids containing an acetyl group on C17.

CONCLUSIONS

The data demonstrate that steroids and analogues differ with respect to conformational changes elicited by these drugs as well as sensitivity to the effects of mutations. Steroids and analogues could be provisionally divided into three major groups based on their actions on the ρ1 GABAA receptor: 5β-reduced uncharged steroids, sulfated and carboxylated steroids, and 17β-estradiol. Further division among 5β-reduced uncharged steroids was based on substituent at position C17.

Neurosteroid interactions with synaptic and extrasynaptic GABA(A) receptors: regulation of subunit plasticity, phasic and tonic inhibition, and neuronal network excitability

RATIONALE

Neurosteroids are steroids synthesized within the brain with rapid effects on neuronal excitability. Allopregnanolone, allotetrahydrodeoxycorticosterone, and androstanediol are three widely explored prototype endogenous neurosteroids. They have very different targets and functions compared to conventional steroid hormones. Neuronal γ-aminobutyric acid (GABA) type A (GABA(A)) receptors are one of the prime molecular targets of neurosteroids.

OBJECTIVE

This review provides a critical appraisal of recent advances in the pharmacology of endogenous neurosteroids that interact with GABA(A) receptors in the brain. Neurosteroids possess distinct, characteristic effects on the membrane potential and current conductance of the neuron, mainly via potentiation of GABA(A) receptors at low concentrations and direct activation of receptor chloride channel at higher concentrations. The GABA(A) receptor mediates two types of inhibition, now characterized as synaptic (phasic) and extrasynaptic (tonic) inhibition. Synaptic release of GABA results in the activation of low-affinity γ2-containing synaptic receptors, while high-affinity δ-containing extrasynaptic receptors are persistently activated by the ambient GABA present in the extracellular fluid. Neurosteroids are potent positive allosteric modulators of synaptic and extrasynaptic GABA(A) receptors and therefore enhance both phasic and tonic inhibition. Tonic inhibition is specifically more sensitive to neurosteroids. The resulting tonic conductance generates a form of shunting inhibition that controls neuronal network excitability, seizure susceptibility, and behavior.

CONCLUSION

The growing understanding of the mechanisms of neurosteroid regulation of the structure and function of the synaptic and extrasynaptic GABA(A) receptors provides many opportunities to create improved therapies for sleep, anxiety, stress, epilepsy, and other neuropsychiatric conditions.

Biotransformation of 21-O-acetyl-deoxycorticosterone by cell suspension cultures of Digitalis lanata (strain W.1.4)

Cell cultures of Digitalis species are known to accept exogenous substrates for biotransformation reactions. We here report the biotransformation of 21-O-acetyl-deoxycorticosterone (1) by cell suspension cultures of Digitalis lanata strain W.1.4. Nine derivatives of 1 were obtained and their chemical structures determined by spectroscopic methods. 2β-Hydroxylation and C-21-glucosylation of the steroidal nucleus were described for the first time in suspension-cultured plant cells. Steroid 5α- and 5β-reduction products were also observed. Among the compounds isolated and structures elucidated were 2β,3β,21-trihydroxy-4-pregnen-20-one, 2β,3α,21-trihydroxy-4-pregnen-20-one and 3β,21-dihydroxy-5α-pregnan-20-one-3β-O-β-glucoside.

Defensive effect of natrium diethyldithiocarbamate trihydrate (NDDCT) and lisinopril in DOCA-salt hypertension-induced vascular dementia in rats

RATIONALE

Vascular dementia and hypertension are increasing day by day, with a high degree of co-occurrence. Tremendous amount of research work is required so that new pharmacological agents may be identified for their appropriate therapeutic utility to combat different dementing disorders.

OBJECTIVES

This study investigates the effect of natrium diethyldithiocarbamate trihydrate (NDDCT), a nuclear factor kappa-B (NF-κB) inhibitor, as well as lisinopril, an angiotensin converting enzyme (ACE) inhibitor, on deoxycorticosterone acetate (DOCA) hypertension-induced vascular dementia in rats.

METHODS

DOCA was used to induce hypertension and associated vascular dementia. Morris water maze (MWM) was used for testing learning and memory. Endothelial function was assessed by acetylcholine-induced endothelium-dependent relaxation of aortic strips. Different biochemical estimations were used to assess oxidative stress (aortic superoxide anion, serum and brain thiobarbituric acid reactive species, and brain glutathione), nitric oxide levels (serum nitrite/nitrate), and cholinergic activity (brain acetyl cholinesterase activity).

RESULTS

DOCA treatment significantly raised the mean arterial blood pressure of rats, and these hypertensive rats performed poorly on MWM, reflecting impairment of learning and memory. DOCA treatment also impaired vascular endothelial function and different biochemical parameters. Treatments of NDDCT as well as lisinopril significantly attenuated DOCA hypertension-induced impairment of learning and memory, endothelial dysfunction, and changes in various biochemical levels.

CONCLUSIONS

DOCA-salt hypertension induces vascular dementia in rats. NF-κB as well as ACE inhibitors may be considered as potential pharmacological agents for the management of hypertension-induced vascular dementia.

Tension cost correlates with mechanical and biochemical parameters in different myocardial contractility conditions

OBJECTIVES

Tension cost, the ratio of myosin ATPase activity to tension, reflects the economy of tension development in the myocardium. To evaluate the mechanical advantage represented by the tension cost, we studied papillary muscle contractility and the activity of myosin ATPase in the left ventricles in normal and pathophysiological conditions.

METHODS

Experimental protocols were performed using rat left ventricles from: (1) streptozotocin-induced diabetic and control Wistar rats; (2) N-nitro-L-arginine methyl ester (L-NAME) hypertensive and untreated Wistar rats; (3) deoxycorticosterone acetate (DOCA) salt-treated, nephrectomized and salt- and DOCA-treated rats; (4) spontaneous hypertensive rats (SHR) and Wistar Kyoto (WKY) rats; (5) rats with myocardial infarction and shamoperated rats. The isometric force, tetanic tension, and the activity of myosin ATPase were measured.

RESULTS

The results obtained from infarcted, diabetic, and deoxycorticosterone acetate-salt-treated rats showed reductions in twitch and tetanic tension compared to the control and sham-operated groups. Twitch and tetanic tension increased in the N-nitro-L-arginine methyl ester-treated rats compared with the Wistar rats. Myosin ATPase activity was depressed in the infarcted, diabetic, and deoxycorticosterone acetate salt-treated rats compared with control and sham-operated rats and was increased in N-nitro-L-arginine methyl ester-treated rats. These parameters did not differ between SHR and WKY rats. In the studied conditions (e.g., post-myocardial infarction, deoxycorticosterone acetate salt-induced hypertension, chronic N-nitro-L-arginine methyl ester treatment, and streptozotocin-induced diabetes), a positive correlation between force or plateau tetanic tension and myosin ATPase activity was observed.

CONCLUSION

Our results suggest that the myocardium adapts to force generation by increasing or reducing the tension cost to maintain myocardial contractility with a better mechanical advantage.

Excretion of norsteroids' phase II metabolites of different origin in human

The urinary phase II metabolites of norsteroids, 19-norandrosterone, 19-noretiocholanolone and 19-norepiandrosterone glucuronide and sulphate, were analyzed in samples collected during the pregnancy, following the administration of norsteroids or the consumption of edible parts of non-castrated pig and in athletes' samples in which they were found during routine controls. The level of the sulfo- and glucuroconjugated metabolites was precisely determined by GC/HRMS, after selective hydrolysis. The goal was to evaluate whether the fine analysis of the norsteroid conjugates produced and excreted in different conditions would show a pattern that could be linked to their origin. The delta (13)C values of the metabolites formed following the ingestion of edible parts of non-castrated pig were measured by isotope ratio mass spectrometry. Our results indicated that it is not possible to determine the origin of the urinary metabolites based upon the sole evaluation of the different metabolites and conjugates. The GC/C/IRMS is the only method permitting to distinguish between the exogenous and endogenous origin of the metabolites.

The neurosteroid system: an emerging therapeutic target for hepatic encephalopathy

Both acute and chronic liver failure induce cerebral complications known as hepatic encephalopathy (HE) and thought to selectively involve brain astrocytes. Alterations of astrocytic-neuronal cross talk occurs affecting brain function. In acute liver failure, astrocyte undergo swelling, which results in increased intracranial pressure and may lead to brain herniation. In chronic liver failure, Alzheimer-type II astrocytosis is a characteristic change. Neurosteroids (NS) synthesized in the brain mainly by astrocytes independent of peripheral steroidal sources (adrenals and gonads) are suggested to play a role in HE. NS bind and modulate different types of membrane receptors. Effects on the gamma amino butyric acid (GABA)-A receptor complex are the most extensively studied. For example, the NS tetrahydroprogesterone (allopregnanolone), and tetrahydrodeoxycorticosterone (THDOC) are potent positive allosteric modulators of GABA-A receptors. As a consequence of modulation of these receptors, NS are well-known to modulate inhibitory neurotransmission in the central nervous system. Some NS bind to intracellular receptors, and in this way may also regulate gene expression. In HE, it has been well documented that neurotransmission and gene expression alterations occur during the progression of the disease. This review summarizes findings of relevance for the involvement of NS in human and experimental HE.

Steroid regulation of the GABAA receptor: ligand binding, chloride transport and behaviour

Certain endogenous steroids are modulators of GABAA receptors. Tetrahydroprogesterone (THP, 5 alpha-pregnan-3 alpha-ol-20-one) and tetrahydrodeoxy-corticosterone (THDOC, 5 alpha-pregnane-3 alpha, 21-diol-20-one) behave as allosteric agonists of GABAA receptors whereas pregnenolone sulphate acts as an antagonist. THP and THDOC modulate ligand binding to GABAA receptors like barbiturates; they potentiate binding of the GABAA receptor agonist muscimol and the benzodiazepine flunitrazepam and they allosterically inhibit binding of the convulsant t-butylbicyclophosphorothionate. THP and THDOC also stimulate chloride uptake and currents in synaptoneurosomes and neurons. Pregnenolone sulphate acts principally as an allosteric GABAA receptor antagonist; it competitively inhibits binding of [35S] TBPS and blocks GABA agonist-activated Cl- uptake and currents in synaptoneurosomes and neurons. In behavioural experiments the GABA-agonistic steroid THDOC shows anxiolytic actions whereas the GABA-antagonistic steroid pregnenolone sulphate antagonizes barbiturate-induced hypnosis. Changes in physiological levels of GABAergic steroids may alter GABAA receptor function, influencing neuronal excitability and CNS arousal. For example, pregnancy and the puerperium are associated with alterations in GABAA receptor binding which might be attributable to steroid actions.

Steroid modulation of the GABAA receptor complex: electrophysiological studies

The effect of some endogenous and synthetic steroids on the operation of inhibitory and excitatory amino acid neurotransmitter receptors was examined. Anaesthetic pregnane steroids (e.g. alphaxalone, 5 alpha-pregnan-3 alpha-ol-20-one, 5 alpha-pregnane-3 alpha,21-diol-20-one) potentiated GABAA receptor-mediated whole-cell currents recorded from bovine chromaffin cells. The threshold concentration for enhancement was 10-30 nM. Potentiation was stereoselective and was mediated by a steroid-induced prolongation of the burst duration of the GABA-activated channel. Additionally, the pregnane steroids directly activated the GABAA receptor. Both the potentiation and activation appear to be mediated through a site(s) distinct from the well-known barbiturate and benzodiazepine allosteric sites of the GABAA receptor. Intracellularly applied alphaxalone and 5 beta-pregnan-3 alpha-ol-20-one had no discernible effects on the GABAA receptor, suggesting that the steroid binding site can only be accessed extracellularly. Unlike behaviourally depressant barbiturates, which modulate GABAA receptor function in a manner similar to that of the pregnane steroids, alphaxalone and 5 beta-pregnan-3 alpha-ol-20-one show striking pharmacological selectivity. Voltage-clamp recordings from rat central neurons in culture indicate that pentobarbitone exerts its potentiating and GABA-mimetic effects over a range of concentrations which also depress currents mediated by glutamate receptor subtypes. In contrast, alphaxalone and several endogenous steroids greatly enhance responses to GABA, but have no direct effect on glutamate receptors. Such pharmacological selectivity, coupled with appropriate stereoselectivity of action, suggests that the GABAA receptor mediates some of the behavioural effects of synthetic and endogenous pregnane steroids.

PKC activation sets an upper limit to the functional plasticity of GABAergic transmission induced by endogenous neurosteroids

The activity of GABAergic inhibitory interneurones located in lamina II of the spinal cord is of fundamental importance for the processing of peripheral nociceptive messages. We have recently shown that 3alpha-hydroxy ring A-reduced pregnane neurosteroids [3alpha5alpha-neurosteroids (3alpha5alphaNS)], potent allosteric modulators of GABA(A) receptors (GABA(A)Rs), are synthesized in the spinal cord and limit thermal hyperalgesia during inflammatory pain. Because changes in the expression of calcium-dependent protein kinases [protein kinase C (PKC)] are observed during pathological pain in the spinal cord, we examined the possible interactions between PKC and 3alpha5alphaNS at synaptic GABA(A)Rs. Using patch-clamp recordings of lamina II interneurones in the spinal cord of 15-20-day-old rats, we showed that synaptic inhibition mediated by GABA(A)Rs and its modulation by 3alpha5alphaNS in lamina II of the spinal cord largely depend on activation of PKC. Our experimental results suggested that activation of PKC locks synaptic GABA(A)Rs in a functional state precluding further positive allosteric modulation by endogenous and exogenous 3alpha5alphaNS. This effect was fully prevented by coadministration of chelerythrin, an inhibitor of PKC. Furthermore, application of chelerythrin alone rendered synaptic GABA(A)Rs hypersensitive to endogenously produced or exogenously applied 3alpha5alphaNS. These findings confirmed that there was a significant production of endogenous 3alpha5alphaNS in lamina II of the spinal cord but also indicated that PKC-dependent phosphorylation processes were tonically activated to control GABA(A)R-mediated inhibition under resting conditions. We therefore can conclude that PKC activation sets an upper limit to the functional plasticity of GABAergic transmission induced by endogenous neurosteroids.

Altered localization of GABA(A) receptor subunits on dentate granule cell dendrites influences tonic and phasic inhibition in a mouse model of epilepsy

Complex changes in GABA(A) receptors (GABA(A)Rs) in animal models of temporal lobe epilepsy during the chronic period include a decrease in the delta subunit and increases in the alpha4 and gamma2 subunits in the dentate gyrus. We used postembedding immunogold labeling to determine whether the subcellular locations of these subunits were also altered in pilocarpine-treated epileptic mice, and related functional changes were identified electrophysiologically. The ultrastructural studies confirmed a decrease in delta subunit labeling at perisynaptic locations in the molecular layer of the dentate gyrus where these subunits are critical for tonic inhibition. Unexpectedly, tonic inhibition in dentate granule cells was maintained in the epileptic mice, suggesting compensation by other GABA(A)Rs. An insensitivity of the tonic current to the neurosteroid tetrahydrodeoxy-corticosterone was consistent with decreased expression of the delta subunit. In the pilocarpine-treated mice, alpha4 subunit labeling remained at perisynaptic locations, but increased gamma2 subunit labeling was also found at many perisynaptic locations on granule cell dendrites, consistent with a shift of the gamma2 subunit from synaptic to perisynaptic locations and potential partnership of the alpha4 and gamma2 subunits in the epileptic animals. The decreased gamma2 labeling near the center of synaptic contacts was paralleled by a corresponding decrease in the dendritic phasic inhibition of granule cells in the pilocarpine-treated mice. These GABA(A)R subunit changes appear to impair both tonic and phasic inhibition, particularly at granule cell dendrites, and could reduce the adaptive responses of the GABA system in temporal lobe epilepsy.

Acute effects of neurosteroids in a rodent model of primary paroxysmal dystonia

The pathophysiology of various types of dyskinesias, including dystonias, is poorly understood. Clinical and epidemiological studies in humans revealed that the severity of dyskinesias and the frequency of paroxysmal forms of the disease are altered by factors such as the onset of puberty, pregnancy, cyclical changes and stress, indicating an underlying hormonal component. The dystonic phenotype in the dt(sz) hamster, a genetic animal model of paroxysmal dystonia, has been suggested to be based on a deficit of striatal gamma-aminobutyric acid (GABA)ergic interneurons and changes in the GABA(A) receptor complex. In this animal model, hormonal influences seem to be also involved in the pathophysiology, but an influence of peripheral sex hormones has already been excluded. Possibly, neurosteroids as endogenous regulators of the GABA(A) receptor may be critically involved in the pathophysiology of dystonia in this animal model. Therefore, in the present study, the effects of the neurosteroids allopregnanolone acetate and allotetrahydrodeoxycorticosterone (THDOC), representing positive modulators of the GABA(A) receptor, as well as of the negative GABA(A) receptor modulators pregnenolone sulfate and dehydroepiandrosterone (DHEA), on severity of dystonia were examined in dt(sz) hamsters after acute intraperitoneal injections. Allopregnanolone acetate and THDOC exerted a moderate reduction of dystonia, whereas pregnenolone sulfate and DHEA had no significant effects. Although the effects of allopregnanolone acetate and THDOC were moderate and short-lasting, the present results suggest that changes in neurosteroid levels might be involved in the initiation of dystonic episodes. Future studies have to include measurements of brain neurosteroid levels as well as of chronic neurosteroid administrations to clarify the pathophysiological role and therapeutic potential of neurosteroids in dystonia.

GABAA and glycine receptor-mediated transmission in rat lamina II neurones: relevance to the analgesic actions of neuroactive steroids

Analgesic neurosteroids such as 5alpha-pregnan-3alpha-ol-20-one (5alpha3alpha) are potent selective endogenous modulators of the GABA(A) receptor (GABA(A)R) while certain synthetic derivatives (i.e. minaxolone) additionally enhance the function of recombinant glycine receptors (GlyR). Inhibitory transmission within the superficial dorsal horn has been implicated in mediating the analgesic actions of neurosteroids. However, the relative contribution played by synaptic and extrasynaptic receptors is unknown. In this study, we have compared the actions of 5alpha3alpha and minaxolone upon inhibitory transmission mediated by both GABA(A) and strychnine-sensitive GlyRs in lamina II neurones of juvenile (P15-21) rats. At the near physiological temperature of 35 degrees C and at a holding potential of -60 mV we recorded three kinetically distinct populations of miniature IPSCs (mIPSCs): GlyR-mediated, GABA(A)R-mediated and mixed GABA(A)R-GlyR mIPSCs, arising from the corelease of both inhibitory neurotransmitters. In addition, sequential application of strychnine and bicuculline revealed a small (5.2 +/- 1.0 pA) GlyR- but not a GABA(A)R-mediated tonic conductance. 5alpha3alpha (1-10 microm) prolonged GABA(A)R and mixed mIPSCs in a concentration-dependent manner but was without effect upon GlyR mIPSCs. In contrast, minaxolone (1-10 microm) prolonged the decay of GlyR mIPSCs and, additionally, was approximately 10-fold more potent than 5alpha3alpha upon GABA(A)R mIPSCs. However, 5alpha3alpha and minaxolone (1 microm) evoked a similar bicuculline-sensitive inhibitory conductance, indicating that the extrasynaptic GABA(A)Rs do not discriminate between these two steroids. Furthermore, approximately 92% of the effect of 1 microm 5alpha3alpha upon GABAergic inhibition could be accounted for by its action upon the extrasynaptic conductance. These findings are relevant to modulation of inhibitory circuits within spinally mediated pain pathways and suggest that extrasynaptic GABA(A)Rs may represent a relevant molecular target for the analgesic actions of neurosteroids.

Neurosteroid modulation of neuronal excitability and synaptic transmission in the rat medial vestibular nuclei

In rat brainstem slices, we investigated the influence of the neurosteroids tetrahydrodeoxycorticosterone (THDOC) and allopregnanolone (ALLO) on the synaptically driven and spontaneous activity of vestibular neurons, by analysing their effects on the amplitude of the field potentials evoked in the medial vestibular nuclei (MVN) by vestibular afferent stimulation and on the spontaneous firing rate of MVN neurons. Furthermore, the interaction with gamma-aminobutyric acid (GABA) and glutamate receptors was analysed by using specific antagonists for GABA(A) (bicuculline), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/ kainate [2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo(f)quinoxaline-7-sulphonamide disodium salt (NBQX)], N-methyl-D-aspartate (NMDA) [D-(-)-2-amino-5-phosphonopentanoic acid (AP-5)] and group I metabotropic glutamate receptors (mGlu-I) [(R,S)-1-aminoindan-1,5-dicarboxylic acid (AIDA)] receptors. THDOC and ALLO evoked two opposite long-lasting effects, consisting of either a potentiation or a reduction of field potential and firing rate, which showed early and late components, occurring in conjunction or separately after neurosteroid application. The depressions depended on GABA(A) receptors, as they were abolished by bicuculline, while early potentiation involved glutamate AMPA/kainate receptors, as NBQX markedly reduced the incidence of early firing rate enhancement and, in the case of ALLO, even provoked depression. This suggests that THDOC and ALLO enhance the GABA(A) inhibitory influence on the MVN neurons and facilitate the AMPA/kainate facilitatory one. Conversely, a late potentiation effect, which was still induced after glutamate and GABA(A) receptor blockade, might involve a different mechanism. We conclude that the modulation of neuronal activity in the MVN by THDOC and ALLO, through their actions on GABA(A) and AMPA/kainate receptors, may have a physiological role in regulating the vestibular system function under normal conditions and during the stress response that accompanies many forms of vestibular dysfunction.

Rat alpha6beta2delta GABAA receptors exhibit two distinct and separable agonist affinities

The onset of motor learning in rats coincides with exclusive expression of GABAA receptors containing alpha6 and delta subunits in the granule neurons of the cerebellum. This development temporally correlates with the presence of a spontaneously active chloride current through alpha6-containing GABAA receptors, known as tonic inhibition. Here we report that the coexpression of alpha6, beta2, and delta subunits produced receptor-channels which possessed two distinct and separable states of agonist affinity, one exhibiting micromolar and the other nanomolar affinities for GABA. The high-affinity state was associated with a significant level of spontaneous channel activity. Increasing the level of expression or the ratio of beta2 to alpha6 and delta subunits increased the prevalence of the high-affinity state. Comparative studies of alpha6beta2delta, alpha1beta2delta, alpha6beta2gamma2, alpha1beta2gamma2 and alpha4beta2delta receptors under equivalent levels of expression demonstrated that the significant level of spontaneous channel activity is uniquely attributable to alpha6beta2delta receptors. The pharmacology of spontaneous channel activity arising from alpha6beta2delta receptor expression corresponded to that of tonic inhibition. For example, GABAA receptor antagonists, including furosemide, blocked the spontaneous current. Further, the neuroactive steroid 5alpha-THDOC and classical glycine receptor agonists beta-alanine and taurine directly activated alpha6beta2delta receptors with high potency. Specific mutation within the GABA-dependent activation domain (betaY157F) impaired both low- and high-affinity components of GABA agonist activity in alpha6betaY157Fdelta receptors, but did not attenuate the spontaneous current. In comparison, a mutation located between the second and third transmembrane segments of the delta subunit (deltaR287M) significantly diminished the nanomolar component and the spontaneous activity. The possibility that the high affinity state of the alpha6beta2delta receptor modulates the granule neuron activity as well as potential mechanisms affecting its expression are discussed.

Neurosteroid synthesis-mediated regulation of GABA(A) receptors: relevance to the ovarian cycle and stress

Recently, we demonstrated cyclic alterations in GABA(A) receptor (GABA(A)R) subunit composition over the ovarian cycle correlated with fluctuations in progesterone levels. However, it remains unclear whether this physiological regulation of GABA(A)Rs is directly mediated by hormones. Here, we show that both ovarian and stress hormones are capable of reorganizing GABA(A)Rs by actions through neurosteroid metabolites. The cyclic alterations in GABA(A)Rs demonstrated in female mice can be mimicked with exogenous progesterone treatment in males or in ovariectomized females. Progesterone (5 mg/kg, twice daily) upregulates the expression of GABA(A)R delta subunits and enhances the tonic inhibition mediated by these receptors in dentate gyrus granule cells (DGGCs). These changes in males as well as ovarian cycle-induced changes in females can be blocked by finasteride, an antagonist of neurosteroid synthesis from progesterone. The altered GABA(A)R expression is unaffected by the progesterone receptor antagonist RU486 [mifepristone (11beta-[p-(dimethylamino)phenyl]-17beta-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one)], suggesting that neurosteroid synthesis and not progesterone receptor activation underlies the hormone-mediated effects on GABA(A)R expression. Neurosteroids can alter GABA(A)R expression on a rapid timescale, because GABA(A)R upregulation can be induced in brain slices maintained in vitro after a short (30 min) treatment with the neurosteroid 3alpha,5alpha-tetrahydrodeoxycorticosterone (THDOC) (100 nM). Consistent with these rapid alterations, acute stress, a condition known to quickly raise THDOC levels, within 30 min induces upregulation of GABA(A)R delta subunit expression and increase tonic inhibition in DGGCs. These results reveal that several physiological conditions characterized by elevations in neurosteroid levels induce a reorganization of GABA(A)Rs through the action of neurosteroids.

The neurosteroid THDOC differentially affects spatial behavior and anesthesia in Slow and Fast kindling rat strains

Rats selectively bred for "Fast" or "Slow" kindling epileptogenesis express different GABA(A) receptor subunits that may account for differences in their miniature inhibitory postsynaptic currents (mIPSCs). The neurosteroid tetrahydrodeoxycorticosterone (THDOC), an endogenous modulator of GABA-mediated inhibition with anesthetic properties and effects on mnemonic processes, preferentially enhances the mIPSCs recorded from the interneurons of Fast rats. Here we show that the anesthetic effect of 20 mg/kg THDOC was reduced in Fast compared to Slow rats. Further, as the strains have previously been shown to differ in their spatial learning abilities, we subsequently examined the effect of a lower dose (5 mg/kg) of THDOC on their performance in the Morris water maze using a matching-to-place paradigm. THDOC injection deteriorated the usually superior mnemonic capabilities of the Slow rats, i.e., concept learning as well as working and reference memory, while marginally improving these behaviors in Fast rats. These outcomes may reflect the divergent expression of GABAA receptors or disinhibition on interneurons versus principal cells that have been observed between the two strains. Possible mechanisms are discussed.

Endogenous neurosteroids regulate GABAA receptors through two discrete transmembrane sites

Inhibitory neurotransmission mediated by GABA(A) receptors can be modulated by the endogenous neurosteroids, allopregnanolone and tetrahydro-deoxycorticosterone. Neurosteroids are synthesized de novo in the brain during stress, pregnancyand after ethanol consumption, and disrupted steroid regulation of GABAergic transmission is strongly implicated in several debilitating conditions such as panic disorder, major depression, schizophrenia, alcohol dependence and catamenial epilepsy. Determining how neurosteroids interact with the GABA(A) receptor is a prerequisite for understanding their physiological and pathophysiological roles in the brain. Here we identify two discrete binding sites in the receptor's transmembrane domains that mediate the potentiating and direct activation effects of neurosteroids. They potentiate GABA responses from a cavity formed by the alpha-subunit transmembrane domains, whereas direct receptor activation is initiated by interfacial residues between alpha and beta subunits and is enhanced by steroid binding to the potentiation site. Thus, significant receptor activation by neurosteroids relies on occupancy of both the activation and potentiation sites. These sites are highly conserved throughout the GABA(A )receptor family, and their identification provides a unique opportunity for the development of new therapeutic, neurosteroid-based ligands and transgenic disease models of neurosteroid dysfunction.

Relationship between omega-3 fatty acids and plasma neuroactive steroids in alcoholism, depression and controls

Deficiency in the long-chain omega-3 fatty acid, docosahexaenoic acid (DHA) has been associated with increased corticotropin releasing hormone and may contribute to hypothalamic pituitary axis (HPA) hyperactivity. Elevated levels of the neuroactive steroids, allopregnanolone (3alpha,5alpha-THP) and 3alpha,5alpha-tetrahydrodeoxycorticosterone (THDOC) appear to counter-regulate HPA hyperactivity. Plasma essential fatty acids and neurosteroids were assessed among 18 male healthy controls and among 34 male psychiatric patients with DSM-III alcoholism, depression, or both. Among all subjects, lower plasma DHA was correlated with higher plasma THDOC (r = -0.3, P < 0.05) and dihydroprogesterone (DHP) (r = -0.52, P < 0.05). Among psychiatric patients lower DHA was correlated with higher DHP (r = -0.60, P < 0.01), and among healthy controls lower plasma DHA was correlated with higher THDOC (r = -0.83, P < 0.01) and higher isopregnanolone (3beta,5alpha-THP) (r = -0.55, P < 0.05). In this pilot observational study, lower long-chain omega-3 essential fatty acid status was associated with higher neuroactive steroid concentrations, possibly indicating increased feedback inhibition of the HPA axis.

Inhibition by alpha-tetrahydrodeoxycorticosterone (THDOC) of pre-sympathetic parvocellular neurones in the paraventricular nucleus of rat hypothalamus

BACKGROUND AND PURPOSE

alpha-tetrahydrodeoxycorticosterone (THDOC) is an endogenous neuroactive steroid which increases in plasma and brain concentration during stress. It has both positive and negative modulatory effects on GABA activated GABAA currents, dependent upon the dose. We investigated the effects of THDOC on spinally-projecting "pre-sympathetic" neurones in the parvocellular subnucleus of the hypothalamic paraventricular nucleus (PVN), to determine whether it activates or inhibits these neurones, and by what mechanism.

EXPERIMENTAL APPROACH

Rat spinally-projecting (parvocellular) PVN neurones were identified by retrograde labelling and the action of THDOC investigated with three modes of patch-clamp: cell-attached action current, whole-cell voltage-clamp and cell-attached single-channel recording.

KEY RESULTS

In cell-attached patch mode, parvocellular neurones fired action potentials spontaneously with an average frequency of 3.6 +/- 1.1 Hz. Bath application of THDOC reduced this with an EC50 of 67 nM (95% confidence limits: 54 to 84 nM), Hill coefficient 0.8 +/- 0.04, n = 5. In whole-cell patch-clamp mode, pressure ejection of GABA evoked inward currents. These were clearly GABAA currents, since they were inhibited by the GABAA receptor antagonist bicuculline, and reversed near the chloride equilibrium potential. THDOC significantly potentiated GABAA currents (1 microM THDOC: 148 +/- 15% of control, n = 5, p < or = 0.05, ANOVA). Single-channel analysis showed no differences in conductance or corrected mean open times in the presence of 1 microM THDOC.

CONCLUSIONS AND IMPLICATIONS

THDOC inhibited parvocellular neuronal activity without showing any evidence of the bidirectional activity demonstrated previously with cultured hypothalamic neurones. Our data are consistent with the hypothesis that THDOC acts by potentiating the post-synaptic activity of endogenously released GABA.

Molecular basis for the GABAA receptor-mediated tonic inhibition in rat somatosensory cortex

Fast inhibitory synaptic transmission is primarily mediated by synaptically released gamma-aminobutyric acid (GABA) acting on postsynaptic GABA(A) receptors. GABA acting on GABA(A) receptors produces not only phasic but also tonic inhibitions by persistent activation of extrasynaptic receptors. However, the mechanistic characteristics of tonic inhibition in the neocortex are not well-understood. To address this, we studied pharmacologically isolated GABA(A) receptor-mediated currents in neocortical pyramidal neurons in rat brain slices. Bath application of bicuculline blocked miniature inhibitory postsynaptic currents (mIPSCs) and produced an outward shift in baseline holding current (I(hold)). Low concentrations of SR95531, a competitive GABA(A) receptor antagonist, abolished mIPSCs but had no significant effect on I(hold). The benzodiazepine midazolam produced an inward shift in I(hold) by augmenting tonic GABA(A) receptor-mediated currents, which were significantly greater in layer V neurons than in layer II/III. Single-cell reverse transcriptase-polymerase chain reaction (RT-PCR) revealed a relatively higher expressions of alpha1 and alpha5 subunit mRNA in layer V neurons. L-655708, an alpha5 subunit-specific inverse agonist, reduced tonic currents in layer V but not in layer II/III neurons, whereas zolpidem, an alpha1-subunit agonist, exerted equivalent effects in both layers. These data suggest that the alpha1 GABA(A) receptor subunit is generally involved in tonic inhibition in pyramidal neurons of the neocortex, whereas the alpha5 subunit is specifically involved in layer V neurons.

Olanzapine and fluoxetine administration and coadministration increase rat hippocampal pregnenolone, allopregnanolone and peripheral deoxycorticosterone: implications for therapeutic actions

Olanzapine and fluoxetine elevate the GABAergic neuroactive steroid allopregnanolone to physiologically relevant concentrations in rodent cerebral cortex. It is unknown if these agents also alter pregnenolone or deoxycorticosterone. Since olanzapine and fluoxetine in combination have clinical utility and may demonstrate synergistic effects, we investigated neuroactive steroid alterations following olanzapine, fluoxetine or coadministration. Male rats received IP vehicle, olanzapine, fluoxetine or the combination of both agents in higher-dose (0, 10, 20 or 10/20 mg/kg, respectively) and lower-dose (0, 5, 10 or 5/10 mg/kg, respectively) experiments. Pregnenolone and allopregnanolone levels in hippocampus were determined by gas chromatography/mass spectrometry. Peripheral deoxycorticosterone and other steroid levels were determined by radioimmunoassay. Olanzapine, fluoxetine or the combination increased hippocampal pregnenolone and serum deoxycorticosterone in both higher- and lower-dose experiments, and elevated hippocampal allopregnanolone in higher-dose conditions. No synergistic effects on pregnenolone or allopregnanolone were observed following olanzapine and fluoxetine coadministration compared to either compound alone. Pregnenolone and its sulfate enhance learning and memory in rodent models, and therefore pregnenolone elevations may be relevant to cognitive changes in psychotic and affective disorders. Since pregnenolone decreases have been linked to depression, it is possible that olanzapine- and fluoxetine-induced pregnenolone elevations may contribute to the antidepressant actions of these agents.

Characterization of brain neurons that express enzymes mediating neurosteroid biosynthesis

Allopregnanolone (ALLO) and tetrahydrodeoxycorticosterone (THDOC) are potent positive allosteric modulators of GABA action at GABA(A) receptors. ALLO and THDOC are synthesized in the brain from progesterone or deoxycorticosterone, respectively, by the sequential action of two enzymes: 5alpha-reductase (5alpha-R) type I and 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD). This study evaluates 5alpha-R type I and 3alpha-HSD mRNA expression level in mouse brain by using in situ hybridization combined with glutamic acid decarboxylase 67/65, vesicular glutamate transporter 2, glial fibrillary acidic protein, and S100beta immunohistochemistry. We demonstrate that 5alpha-R type I and 3alpha-HSD colocalize in cortical, hippocampal, and olfactory bulb glutamatergic principal neurons and in some output neurons of the amygdala and thalamus. Neither 5alpha-R type I nor 3alpha-HSD mRNAs are expressed in S100beta- or glial fibrillary acidic protein-positive glial cells. Using glutamic acid decarboxylase 67/65 antibodies to mark GABAergic neurons, we failed to detect 5alpha-R type I and 3alpha-HSD in cortical and hippocampal GABAergic interneurons. However, 5alpha-R type I and 3alpha-HSD are significantly expressed in principal GABAergic output neurons, such as striatal medium spiny, reticular thalamic nucleus, and cerebellar Purkinje neurons. A similar distribution and cellular location of neurosteroidogenic enzymes was observed in rat brain. Taken together, these data suggest that ALLO and THDOC, which can be synthesized in principal output neurons, modulate GABA action at GABA(A) receptors, either with an autocrine or a paracrine mechanism or by reaching GABA(A) receptor intracellular sites through lateral membrane diffusion.

Kindling-induced alterations in GABAAreceptor-mediated inhibition and neurosteroid activity in the rat piriform cortex

The piriform cortex makes strong interconnections with limbic structures (amygdala, entorhinal cortex and hippocampus) that are involved in memory processing. These connections have also been implicated in the development of temporal lobe epilepsy. However, little is known about how neurones in this region may change during seizure genesis. Here we tested the hypothesis that in the kindling model of temporal lobe epilepsy GABAA receptor-mediated inhibition is altered in the piriform cortex. To do this we performed whole-cell patch-clamp recordings in piriform cortex brain slices obtained from non-kindled and amygdala-kindled adult rats. We found that kindling coincided with an increase in the amplitude and duration of miniature inhibitory post-synaptic currents (mIPSCs) recorded from non-pyramidal neurones, whereas the mIPSCs occurring on pyramidal (excitatory) cells did not change. Non-stationary noise analysis of mIPSCs occurring on the non-pyramidal neurones showed that inferred unitary conductance of synaptic channels were the same before and after kindling, implying that the channel number increased significantly. Immunocytochemical analysis of the inhibitory innervation showed that it was also unaltered by seizure induction. We also found that the effect of the positive modulator tetrahydrodeoxycorticosterone was reduced on the pyramidal neurones after kindling. In contrast, the potentiating effects of tetrahydrodeoxycorticosterone on non-pyramidal cells were about the same after kindling as in control (sham) rats. These data indicate that amygdala kindling causes a shift in the inhibition 'balance' between the pyramidal and non-pyramidal cells, perhaps leading to the disinhibition of pyramidal cells.

GABAergic tonic inhibition of substantia gelatinosa neurons in mouse spinal cord

We used whole-cell recording to identify, for the first time, GABAergic tonic current in subpopulations of substantia gelatinosa neurons in mouse spinal cord slices. Application of the gamma-aminobutyric acid type A receptor antagonist bicuculline revealed tonic currents in 49 of 73 substantia gelatinosa neurons. These tonic currents were dissected into three groups according to their diverse pharmacological properties. In the first group, furosemide failed to block the tonic current while midazolam and propofol potentiated it. In the second group, furosemide blocked the tonic current but midazolam and propofol failed to enhance the current. In the third group, furosemide blocked and 3alpha, 21-dihydroxy-5alpha-pregnan-20-one enhanced the tonic current. The presence of mRNAs for alpha4, alpha5, delta and epsilon subunits in the substantia gelatinosa (reverse-transcriptase polymerase chain reaction) suggest that gamma-aminobutyric acid type A receptors comprising alpha5betaxgamma2, alphaxbetaxepsilon and alpha4betaxdelta subunits are responsible for tonic currents.

Plastic neuronal changes in GABA(A) receptor gene expression induced by progesterone metabolites: in vitro molecular and functional studies

Expression of specific gamma-aminobutyric acid type A (GABA(A)) receptor subunit genes in neurons is affected by endogenous modulators of receptor function such as neuroactive steroids. Neuroactive steroids such as the progesterone metabolite allopregnanolone might thus exert differential effects on GABA(A) receptor plasticity in neurons, likely accounting for some of the physiological actions of these compounds. Here we summarise experimental data obtained in vitro that show how fluctuations in the concentration of progesterone regulate both the expression and function of GABA(A) receptors. The data described in this manuscript are in agreement with the notion that fluctuations in the concentrations of progesterone and its metabolite allopregnanolone play a major role in the temporal pattern of expression of various subunits of the GABA(A) receptor. Thus, rapid and long-lasting increases or decreases in the concentrations of these steroid derivatives observed in physiological and patho-physiological conditions, or induced by pharmacological treatments, might elicit selective changes in GABA(A) receptor gene expression and function in specific neuronal populations. Given both the importance of GABA(A) receptors in the regulation of neuronal excitability and the large fluctuations in the plasma and brain concentrations of neuroactive steroids associated with physiological conditions and the response to environmental stimuli, these compounds are likely among the most relevant endogenous modulators that could affect emotional and affective behaviors.

Tonic GABAAreceptor-mediated currents in human brain

GABA(A) receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition. It has been proposed that tonic inhibition plays a critical part in controlling neuronal and network excitability. Although tonic GABA(A) receptor-mediated currents have been well characterized in rodents, their existence in human tissue has yet to be demonstrated. Here we show that tonic currents can be recorded from human tissue obtained from patients undergoing temporal lobectomies. Tonic GABA(A) receptor-mediated currents were present in pyramidal cells and interneurons in layer V-VI of temporal neocortex and granule cells in the dentate gyrus. These tonic currents have cell type-specific pharmacologies, opening up the possibility of targeted therapeutics.

Increased neuroactive steroid concentrations in women with bipolar disorder or major depressive disorder

Changes in the plasma concentrations of neuroactive steroids have been associated with various neuropsychiatric disorders. However, the possible role of neuroactive steroids in bipolar disorder (BD) has remained unknown. We therefore determined the plasma levels of neuroactive steroids during the luteal phase of the menstrual cycle in women with BD or major depressive disorder (MDD). The plasma concentrations of 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THPROG), 3alpha,21-dihydroxy-5alpha-pregnan-20-one, progesterone, and cortisol were determined in 17 outpatients with BD, 14 outpatients with MDD, and 16 healthy control subjects. All patients were in a state of well-being and without relapse or recurrence for at least 3 months. Plasma concentrations of progesterone and 3alpha,5alpha-THPROG were significantly greater in patients than in controls, also being higher in BD patients than in MDD patients. Drug-free patients with BD or MDD showed similar differences in steroid concentrations relative to controls, as did drug-treated patients. Comorbidity with panic disorder, obsessive-compulsive disorder, or eating disorder had no effect on the association of mood disorders with steroid concentrations. Women with BD or MDD in a state of well-being showed higher plasma concentrations of progesterone and 3alpha,5alpha-THPROG in the luteal phase than did healthy controls. These differences did not seem to be attributable simply to drug treatment or to comorbidity with other psychiatric conditions in the patients.

In the ventral tegmental area, progestins have actions at D1 receptors for lordosis of hamsters and rats that involve GABA A receptors

In the ventral tegmental area (VTA), progestins facilitate lordosis via actions at gamma-aminobutyric acid (GABA)(A)/benzodiazepine receptor complexes (GBRs) and dopamine type 1 receptors (D1). The relationship between progestins' actions at GBRs and D1 in the VTA for facilitating sexual behavior of hamsters and rats was examined. Ovariectomized (ovx), estradiol (E(2); 10 microg)+progesterone (P; 250 microg; SC)-primed hamsters, with bilateral guide cannulae to the VTA, were pre-tested for sexual and motor behavior and infused with the GBR antagonist bicuculline (100 ng/side) or vehicle. Thirty minutes later, hamsters were re-tested and then infused with the D1 agonist SKF38393 (100 ng/side) or vehicle. Hamsters were post-tested 30 min later. Ovx, E(2) (10 microg)-primed rats were pre-tested, infused first with bicuculline or vehicle, second with SKF38393 or vehicle, third with 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP; 0, 100, or 200 ng) and were post-tested 10 and 60 min after 3alpha,5alpha-THP infusions. VTA infusions of SKF38393 increased lordosis of hamsters or rats. Bicuculline pretreatment reduced SKF38393- and/or progesterone-mediated increases in lordosis of E2-primed hamsters. In E2-primed rats, bicuculline blocked SKF38393- and/or 3alpha,5alpha-THP-mediated increases in lordosis. There were no effects on motor behavior. Thus, in the VTA, GBR activity modulates D1-mediated actions for lordosis of hamsters and rats.

Neurosteroid modulation of recombinant rat alpha5beta2gamma2L and alpha1beta2gamma2L GABA(A) receptors in Xenopus oocyte

GABA(A) receptors containing alpha(5)-subunit have an important role in cognitive function. As the agonistic effect of 3alpha-hydroxy ring-A reduced steroids depends on subunit combinations of the GABA(A) receptor, the antagonistic effect of pregnenolone sulfate and 3beta-hydroxypregnane steroids may vary between alpha(5)-subunit and alpha(1)-subunit containing receptors. We investigated the effect of agonist and antagonist steroids in the recombinant rat alpha(1)beta(2)gamma(2L) and alpha(5)beta(2)gamma(2L) receptors expressed in Xenopus oocytes using a two electrodes voltage-clamp technique. We did not find any significant difference in potency and efficacy of GABA response between alpha(1)beta(2)gamma(2L) and alpha(5)beta(2)gamma(2L) receptors. Compared to the alpha(1)beta(2)gamma(2L) receptor, a significantly lower degree of desensitization was observed in the alpha(5)beta(2)gamma(2L) receptor. In addition, the potencies of 3alpha-OH-5alpha-pregnan-20-one (3alpha5alphaP), 5alpha-pregnan-3alpha,21-diol-20-one (3alpha5alphaTHDOC) and 5alpha-androstane-3alpha,17beta-diol (3alpha5alphaADL) to enhance GABA response were significantly higher in the alpha(5)beta(2)gamma(2L) receptor, whereas their efficacies remained unchanged between two receptors. In either receptor, the efficacy of 3alpha5alphaTHDOC was significantly higher than 3alpha5alphaP and 3alpha5alphaADL. The efficacies of 5beta-pregnan-3beta,21-diol-20-one(UC1015) and 5alpha-pregnan-3beta,20alpha-diol(UC1019) to inhibit 30 microM GABA response, and the efficacies of 3beta-OH-5beta-pregnan-20-one (UC1014) and 5beta-pregnan-3beta, 20beta-diol (UC1020) to inhibit 3 microM 3alpha5alphaTHDOC+3 microM GABA response were higher in the alpha(5)beta(2)gamma(2L) receptor compared to the alpha(1)beta(2)gamma(2L) receptor. The potencies of pregnenolone sulfate and 3beta-hydroxypregnane steroids to inhibit the GABA response and the 3alpha5alphaTHDOC+GABA response did not vary between two receptors. Interestingly, the potencies and efficacies of pregnenolone sulfate and 3beta-hydroxypregnane steroids to inhibit the GABA response were positively correlated to their potencies and efficacies to inhibit the 3alpha5alphaTHDOC+GABA response. Results from the current study revealed a different modulation pattern by neurosteroids between the alpha(1)beta(2)gamma(2L) and alpha(5)beta(2)gamma(2L) receptor.

Mid-aged and aged wild-type and progestin receptor knockout (PRKO) mice demonstrate rapid progesterone and 3alpha,5alpha-THP-facilitated lordosis

RATIONALE

Progesterone (P) and its 5alpha-reduced metabolite, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP), facilitate sexual behavior of rodents via agonist-like actions at intracellular progestin receptors (PRs) and membrane GABA(A)/benzodiazepine receptor complexes (GBRs), respectively.

OBJECTIVE

Given that ovarian secretion of progestins declines with aging, whether or not senescent mice are responsive to progestins was of interest.

METHODS

Homozygous PR knockout (PRKO) or wild-type mice that were between 10-12 (mid-aged) or 20-24 (aged) months of age were administered P or 3alpha,5alpha-THP, and the effect on lordosis were examined. Effects of a progestin-priming regimen that enhances PR-mediated (experiment 1) or more rapid, PR-independent effects of progestins (experiments 2 and 3) on sexual behavior were examined. Levels of P, 3alpha,5alpha-THP, and muscimol binding were examined in tissues from aged mice (experiment 4).

RESULTS

Wild-type, but not PRKO, mice were responsive when primed with 17beta-estradiol (E(2); 0.5 microg) and administered P (500 microg, subcutaneously). Mid-aged wild-type mice demonstrated greater increases in lordosis 6 h later compared to their pre-P, baseline test than did aged wild-type mice (experiment 1). Lordosis of younger and older wild-type, but not PRKO, mice was significantly increased within 5 min of intravenous (IV) administration of P (100 ng), compared with E(2)-priming alone (experiment 2). However, wild-type and PRKO mice demonstrated significant increases in lordosis 5 min after IV administration of 3alpha,5alpha-THP, an effect which was more pronounced in mid-aged than in aged animals (100 ng-experiment 3). In tissues from aged wild-type and PRKO mice, levels of P, 3alpha,5alpha-THP, and muscimol binding were increased by P administration (experiment 4). PR binding was lower in the cortex of PRKO than that of wild-type mice.

CONCLUSIONS

Mid-aged and aged PRKO and wild-type mice demonstrated rapid P or 3alpha,5alpha-THP-facilitated lordosis that may be, in part, independent of activity at PRs.

Observational study on the stability of the psychological status during normal pregnancy and increased blood levels of neuroactive steroids with GABA-A receptor agonist activity

We investigated whether pregnancy could modify psychological symptoms and whether neuroactive steroids which exert an anti-anxiety effect by acting on the gamma-aminobutyric acid (GABA)-A receptors, are modified during pregnancy in young healthy women. Healthy volunteer women in the Department of Obstetrics and Gynecology at Cagliari University participated in the study. They were divided into women with low (group 1, seven subjects) and high (group 2, seven subjects) psychological score by SCL-90 psychometric scale. Age, body mass index and physiological status of pregnancy did not differ between the groups. The subjects were studied before pregnancy during the follicular phase (FP), and the luteal phase (LP) of the menstrual cycle (MC) and four times during pregnancy (at 14th, 22nd, 30th, and 38th week). SCL-90 psychometric scale, circulating levels of progesterone (P4), 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone, AP), 3alpha,21-dihydroxy-5alpha-pregnan-20-one (allotetrahydrodeoxy-corticosterone, THDOC), cortisol and DHEAS were assayed at each visit. The SCL-90 global score and the intensity of psychological symptoms differ between the groups, but within each group they did not change both during MC and during pregnancy. The DHEAS and cortisol levels did not differ between the groups. DHEAS did not change during the study, whereas cortisol levels increased during pregnancy in both groups. Progesterone, AP, and THDOC levels were higher during LP than during FP and further increased during pregnancy, without any difference between the groups. In conclusion, pregnancy does not seem to interfere with the psychological status of healthy women independently of the psychological basal score. Some neuroactive steroids with anxiolytic activity seem to increase during pregnancy depending on placental function. Their increase could represent some kind of protection against maternal anxiety and stress due to concerns about the pregnancy outcome.

SGK1-dependent cardiac CTGF formation and fibrosis following DOCA treatment

The mineralocorticoids aldosterone and deoxycorticosterone acetate (DOCA) stimulate renal tubular salt reabsorption, increase salt appetite, induce extracellular volume expansion, and elevate blood pressure. Cardiac effects of mineralocorticoids include stimulation of matrix protein deposition leading to cardiac fibrosis, which is at least partially due to the direct action of the hormones on cardiac cells. The signaling mechanisms mediating mineralocorticoid-induced cardiac fibrosis have so far remained elusive. Mineralocorticoids have been shown to upregulate the serum- and glucocorticoid-inducible kinase 1 (SGK1), which participates in the effects of mineralocorticoids on renal tubular Na+ reabsorption and salt appetite. To explore the involvement of SGK1 in the pathogenesis of mineralocorticoid-induced cardiac fibrosis, SGK1 knockout mice (sgk1-/-) and wild-type littermates (sgk1+/+) were implanted a 21-day-release 50-mg DOCA pellet and supplied with 1% NaCl in drinking water for 18 days. This DOCA/high-salt treatment increased blood pressure in both genotypes but led to significant cardiac fibrosis only in sgk1+/+ but not in sgk1-/- mice. According to real-time polymerase chain reaction and Western blotting, DOCA/high-salt treatment enhanced transcript levels and protein expression of cardiac connective tissue growth factor (CTGF) only in sgk1+/+ but not in sgk1-/- mice. Furthermore, DOCA (10 microM) upregulated CTGF expression and enhanced CTGF promoter activity in lung fibroblasts isolated from sgk1+/+ but not from sgk1-/- mice, an effect involving spironolactone-sensitive mineralocorticoid receptors and activation of nuclear factor-kappaB (NFkappaB). Our results suggest that SGK1 plays a decisive role in mineralocorticoid-induced CTGF expression and cardiac fibrosis.

Increased levels of pregnenolone and its neuroactive metabolite allopregnanolone in autopsied brain tissue from cirrhotic patients who died in hepatic coma

It has been suggested that neurosteroids with agonist properties at the central GABA-A receptor are implicated in the pathogenesis of hepatic encephalopathy (HE) in chronic liver disease. In order to address this issue, gas chromatography/mass spectrometry was used to measure the neurosteroids pregnenolone, allopregnanolone, and tetrahydrodeoxycorticosterone (THDOC) in postmortem brain tissue from controls, cirrhotic patients who died without HE, a patient who died in uremic coma, and cirrhotic patients who died in hepatic coma. Exposure of rat cerebral cortical membranes to brain extracts from hepatic coma patients resulted in a 53% (p < 0.001) increase in binding of [3H]muscimol, a GABA-A receptor ligand. Subsequent GC/MS analysis showed that concentrations of the GABA-A receptor agonist neurosteroid allopregnanolone were significantly increased in brain tissue from hepatic coma patients compared to patients without HE or controls (p < 0.001). Brain allopregnanolone concentrations were significantly correlated with the magnitude of induction of [3H]muscimol binding (r2 = 0.82, p < 0.0001). Concentrations of allopregnanolone comparable to those observed in hepatic coma brains are pathophysiologically relevant. Concentrations of the neurosteroid precursor pregnenolone were also increased in brain tissue from hepatic coma patients, while those of a second neurosteroid THDOC were below the levels of detection in all groups. Brain concentrations of benzodiazepine receptor ligands estimated by radioreceptor assay were not significantly increased in cirrhotic patients with or without hepatic coma. These findings suggest that increased levels of allopregnanolone rather than "endogenous benzodiazepines" offer a cogent explanation for the phenomenon of "increased GABAergic tone" previously proposed in HE.

The acute anticonvulsant effects of deoxycorticosterone in developing rats: role of metabolites and mineralocorticoid-receptor responses

PURPOSE

The mechanisms that mediate the acute anticonvulsant effects of deoxycorticosterone (DOC) were investigated in young rats.

METHODS

Fifteen-day-old rats were pretreated with a variety of compounds, including (a) agonists of the receptors that bind DOC (mineralocorticoid receptors); (b) the DOC 5alpha- and 5alpha-3alpha-reduced metabolites, plus agonists that bind the receptors of the 5alpha-reduced metabolite of DOC (progesterone receptors); and (c) DOC itself in the presence and absence of metabolism and receptor blockers. Fifteen minutes later, pentylenetetrazol (PTZ) was administered, and maximal pentylenetetrazol (MMT) seizure responses were scored.

RESULTS

Agonists of mineralocorticoid receptors increased the latency to forelimb flexion in PTZ seizures and sometimes suppressed the seizures completely. At low, nonconvulsant doses, spironolactone (a mineralocorticoid-receptor antagonist) blocked the anticonvulsant effects of a nonsedating, but not a sedating, dose of DOC. These data suggest the possible direct involvement of mineralocorticoid receptors in the anticonvulsant effects of DOC. At low, nonconvulsant doses, finasteride (which blocks the metabolism of DOC) partially blocked the protective effects of DOC, suggesting the contribution of metabolites to the anticonvulsant actions of DOC. Dihydrodeoxycorticosterone (DHDOC)-the first metabolite of DOC, an agonist at progesterone receptors, and an allosteric modulator of the gamma-aminobutyric acid (GABA)(A) receptor-and tetrahydrodeoxycorticosterone, a secondary metabolite of DOC and an allosteric modulator of the GABA(A) receptor, both blocked MMT seizures.

CONCLUSIONS

These findings suggest that both DOC and its metabolites may contribute to the anticonvulsant effects seen in young rats, perhaps acting via interactions with several different receptors.

Action of two neuroactive steroids against motor seizures induced by pentetrazol in rats during ontogeny

The anticonvulsant action of two neuroactive steroids, 3alpha-hydroxy-5beta-pregnan-20-one (pregnanolone) and triethylammonium 3 alpha-hydroxy-20-oxo-5 alpha-pregnan-21-yl hydrogensuccinate (THDOC-conjugate), was tested against motor seizures induced by pentetrazol in immature rats. Five age groups (7, 12, 18 and 25 days old and adult rats) were pretreated with the steroids in doses from 2.5 to 40 mg/kg i.p. Twenty minutes later pentetrazol (100 mg/kg s.c.) was administered. Minimal seizures (clonic seizures of head and forelimb muscles with preserved righting ability) could be induced in the three older age groups. They were suppressed by pregnanolone in all these tested groups (this effect was best expressed in 18-day-old rats and decreased with age), whereas significant changes in THDOC-conjugate-pretreated animals appeared only in 18-day-old rats. Generalized tonic-clonic seizures were suppressed by both neuroactive steroids in all age groups, this effect being more marked with pregnanolone and again decreased with age. The 7- and 12-day-old rats exhibited higher sensitivity of the tonic phase so that generalized clonic seizures were observed. Duration of the effect was studied in 12- and 25-day-old animals; it was substantially shorter in the older rats than in 12-day-old animals. Both drugs exhibited an anticonvulsant action in developing rats but, unfortunately, their effect was only shortlasting.

Systemic ethanol administration elevates deoxycorticosterone levels and chronic ethanol exposure attenuates this response

Systemic ethanol administration is known to elevate levels of the GABAergic neuroactive steroid 3alpha,21-dihydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THDOC). 3alpha,5alpha-THDOC is synthesized from deoxycorticosterone (DOC) by metabolism in adrenals and brain. The present study investigated DOC levels in plasma and brain following ethanol administration to naïve and ethanol-exposed rats. Rats were administered ethanol (2 g/kg, i.p.) or saline and DOC levels were measured in plasma and brain regions by radioimmunoassay. Chronic ethanol-exposed rats were administered an ethanol challenge (2 g/kg, i.p.) following 15 days of ethanol liquid diet consumption. Ethanol administration markedly increased DOC levels in plasma, cerebral cortex, hippocampus, hypothalamus, cerebellum, and olfactory tubercle of naïve rats. Ethanol challenge produced an attenuated elevation of DOC in rat plasma and brain following chronic ethanol consumption for 2 weeks. These findings suggest that acute ethanol increases DOC levels in ethanol naïve rats and chronic ethanol consumption induces tolerance to ethanol-induced increases in DOC levels.

The delta subunit of gamma-aminobutyric acid type A receptors does not confer sensitivity to low concentrations of ethanol

GABA(A) receptors (GABA(A)Rs) are usually formed by alpha, beta, and gamma or delta subunits. Recently, delta-containing GABA(A)Rs expressed in Xenopus oocytes were found to be sensitive to low concentrations of ethanol (1-3 mM). Our objective was to replicate and extend the study of the effect of ethanol on the function of alpha4beta3delta GABA(A)Rs. We independently conducted three studies in two systems: rat and human GABA(A)Rs expressed in Xenopus oocytes, studied through two-electrode voltage clamp; and human GABA(A)Rs stably expressed in the fibroblast L(tk-) cell line, studied through patch-clamp electrophysiology. In all cases, alpha4beta3delta GABA(A)Rs were only sensitive to high concentrations of ethanol (100 mM in oocytes, 300 mM in the cell line). Expression of the delta subunit in oocytes was assessed through the magnitude of the maximal GABA currents and sensitivity to zinc. Of the three rat combinations studied, alpha4beta3 was the most sensitive to ethanol, isoflurane, and 5alpha-pregnan-3alpha,21-diol-20-one (THDOC); alpha4beta3delta and alpha4beta3gamma(2S) were very similar in most aspects, but alpha4beta3delta was more sensitive to GABA, THDOC, and lanthanum than alpha4beta3gamma(2S) GABA(A)Rs. Ethanol at 30 mM did not affect tonic GABA-mediated currents in dentate gyrus reported to be mediated by GABA(A)Rs incorporating alpha4 and delta subunits. We have not been able to replicate the sensitivity of alpha4beta3delta GABA(A)Rs to low concentrations of ethanol in four different laboratories in independent studies. This suggests that as yet unidentified factors may play a critical role in the ethanol effects on delta-containing GABA(A)Rs.

Anticonvulsant action of three neurosteroids against cortical epileptic afterdischarges in immature rats

Neurosteroids exhibit anticonvulsant action probably by positive modulatory influence on GABA-A receptors. The action of three neurosteroids was tested against cortical epileptic afterdischarges in immature rats with implanted electrodes. Afterdischarges (ADs) were elicited by rhythmic electrical stimulation (biphasic pulses at 8 Hz frequency for 15s) of sensorimotor cortical region with a slightly suprathreshold current intensity. Drugs were administered intraperitoneally after the first afterdischarge and stimulation was repeated five more times with the same intensity. Allopregnanolone in doses of 20 and 30 mg/kg i.p. was found to be active in 12-day-old rats; there was no effect in 18-day-old rats and only a tendency in 25-day-old ones. Therefore, the effects of pregnanolone and a new derivative THDOC-conjugate (20 and 40 mg/kg) were compared with those of allopregnanolone (40 mg/kg) only in 12- and 25-day-old rats in the second part of study. All three neurosteroids blocked progressive prolongation of repeated ADs seen in control 12-day-old rats. In addition, pregnanolone was able to shorten the ADs. In contrast, duration of ADs in 25-day-old animals was significantly shorter than the duration of the first, predrug AD only after administration of the 40 mg/kg dose of pregnanolone; if corresponding ADs in the control and drug groups were compared, pregnanolone and THDOC-conjugate led to significantly shorter ADs, changes after allopregnanolone administration were statistically significant only in the fourth AD. None of the studied neurosteroids was able to suppress movements directly bound to stimulation as well as clonic seizures accompanying afterdischarges. Among the three drugs studied, pregnanolone was found to be the most potent one. As developmental changes are concerned, the youngest animals exhibited the highest sensitivity to anticonvulsant action of neurosteroids.

High affinity, heterogeneous displacement of [H]EBOB binding to cerebellar GABA receptors by neurosteroids and GABA agonists

Heterogeneous binding interactions of cerebellar GABA(A) receptors were investigated with GABA agonists and neurosteroids. GABA(A) receptors of rat cerebellum were labelled with [(3)H]ethynylbicycloorthobenzoate (EBOB), a convulsant radioligand. Saturation analysis revealed a homogenous, nanomolar population of [(3)H]EBOB binding. Both GABA and 5alpha-tetrahydrodeoxycorticosterone (5alpha-THDOC) displaced [(3)H]EBOB binding heterogeneously, with nanomolar and micromolar potencies. The nanomolar phase of displacement by GABA was selectively abolished by 100 microM furosemide. Physiological concentrations of allopregnanolone (8 nM) and 5alpha-THDOC (20 nM) increased the displacing effects of nanomolar GABA. GABA (0.3 microM ) and 5alpha-THDOC (0.3 microM ) potentiated the micromolar population of displacement by the other. Taurine inhibited [(3)H]EBOB binding also heterogeneously, with micromolar and millimolar potencies, and 0.3 microM 5alpha-THDOC potentiated this inhibition. 5beta-THDOC did not affect [(3)H]EBOB binding significantly but in 1 microM it antagonised selectively the nanomolar displacement by 5alpha-THDOC. [(3)H]EBOB binding to hippocampal GABA(A) receptors was inhibited by GABA and allopregnanolone with low (micromolar) potencies and with slope values higher than unity referring to allosteric interaction. High affinity displacement of cerebellar [(3)H]EBOB binding by GABA agonists and neurosteroids can be associated with constitutively open alpha(6)betadelta GABA(A) receptors, tonic GABAergic inhibitory neurotransmission and its modulation by physiological concentrations of neurosteroids.

6,19-Sulfur-Bridged Progesterone Analogues with Antiimmunosuppressive Activity

Sulfur-bridged pregnanes 6,19-epithioprogesterone, 21-hydroxy-6,19-epithioprogesterone, and the corresponding sulfoxides and sulfones were synthesized and tested as blockers of the immunosuppresive activity of dexamethasone in rat thymocytes. A new one-pot procedure is described for the preparation of 6,19-epithioprogesterone and related compounds by iodocyclization of a 19-sulfanylpregn-5-ene. Antiimmunosuppresive activity was evaluated by the ability of the different steroids to block dexamethasone-mediated apoptosis in thymocytes and dexamethasone-mediated inhibition of the NFkappa-B transcription factor activity. DNA fragmentation and annexin V-FITC positive cells were taken as parameters of apoptosis whereas NFkappa-B activity was tested by the expression of the reporter vector kappaB-luciferase by TNF-alpha in Hela cells. 21-Hydroxy-6,19-epithioprogesterone S,S-dioxide had improved activity in both parameters, while 21-hydroxy-6,19-epithioprogesterone had improved activity only in blocking dexamethasone-induced programmed cell death.